Flat-type (flat panel) display devices are studied in various ways as an image display device for replacing a currently main-stream cathode ray tube (CRT). As such flat-type display devices, for example, there are a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display (PDP). Further, there is also proposed a cold cathode field emission display capable of emitting electrons from a solid to a vacuum space without relying on thermal excitation, a so-called field emission display (FED). The cold cathode field emission display is attracting attention from the viewpoint of a bright screen and low power consumption.
FIG. 7 shows a typical constitution example of the cold cathode field emission display (to be sometimes referred to as “display” hereinafter), and FIG. 8 shows a schematic exploded perspective view of part of a cathode panel 10 and an anode panel 20. In the display, the cathode panel 10 and the anode panel 20 are arranged so as to face each other, and bonded to each other in circumferential regions through a frame (not shown) to constitute a vacuum space of a closed space between these two panels 10 and 20. The cathode panel 10 has a plurality of cold cathode field emission devices (to be sometimes abbreviated as “field emission device” hereinafter). As an example of the field emission device, FIG. 7 shows a so-called Spindt-type field emission device having an electron emitting portion 16 constituted of a conical electron emission electrode 16A. The Spindt-type field emission device comprises a stripe-shaped cathode electrode 12 formed on a first support member 11, an insulating layer 13, a stripe-shaped gate electrode 14 formed on the insulating layer 13, and a conical electron emission electrode 16A formed in an opening portion 15 made through the gate electrode 14 and the insulating layer 13. Generally, many electron emission electrodes 16A are provided so as to correspond to one phosphor layer 22 to be described later. A relatively negative voltage (scanning signal) is applied to the electron emission electrodes 16A from a cathode-electrode driving circuit 25 through the cathode electrode 12, and a relatively positive voltage (video signal) is applied to the gate electrode 14 from a gate-electrode driving circuit 26. Electrons are emitted from the tip of the electron emission electrode 16A on the basis of a quantum tunnel effect depending upon an electric field caused by the voltage applications. The field emission device is not limited to the above Spindt-type field emission device and, in some cases, is selected from field emission devices of various types such as so-called edge-type, flat-type or some other type field emission devices.
The anode panel 20 comprises a plurality of phosphor layers 22 (phosphor layers 22R, 22G, 22B) formed in a matrix or stripe shape on a second support member 21 made of glass and the like, a black matrix 23 filled between the phosphor layers 22, and an anode electrode 24 formed entirely on the phosphor layers 22 and the black matrix 23. A positive voltage higher than a voltage to be applied to the gate electrode 14 is applied to the anode electrode 24 from an anode-electrode driving circuit 27, and the anode electrode 24 works to guide electrons emitted into the vacuum space from the electron emission electrodes 16A to the phosphor layers 22. Further, the anode electrode 24 protects the phosphor particles constituting the phosphor layers 22 from sputtering with particles such as ions. Further, it also works to reflect light, which is emitted from the phosphor layers 22 by electron excitation, towards the second support member 21 to improve the brightness of a display screen. viewed from outside of the second support member 21. The anode electrode 21 is formed, for example, of an aluminum thin film.
Generally, the cathode electrode 12 and the gate electrode 14 are formed in the form of a stripe each in directions in which projection images of these electrodes 12 and 14 cross each other at right angles, and a plurality of field emission devices are provided in an overlap region of the projection images of the electrodes 12 and 14 (the overlap region corresponds to a region of one pixel in a monochromatic display or one subpixel of three subpixels constituting one pixel in a color display). Further, such overlap regions are arranged in the form of a two-dimensional matrix in an effective field (field that works as an actual display screen) of the cathode panel 10. One pixel is constituted of one group of field emission devices arranged in the overlap region of the cathode electrode 12 and the gate electrode 14 on the cathode panel side and the phosphor layer 22 that faces the group of these field emission devices and is on the anode panel side. In the effective field, such pixels are arranged in the order of hundreds of thousands to several millions.
The cathode panel 10 having a number of such field emission devices formed thereon and the anode panel 20 are combined, whereby a display shown in FIGS. 7 and 8 can be obtained. Specifically, an approximately 1 mm high frame (not shown) made of ceramic or glass is prepared. The frame, the cathode panel 10 and the anode panel 20 are attached and bonded with a frit glass, and the frit glass is dried, followed by calcining at approximately 450° C. for 10 to 30 minutes. Then, the inside of the display is vacuumed to a vacuum degree of approximately 10−4 Pa, followed by sealing by a proper method. Alternatively, the frame, the cathode panel 10 and the anode panel 20 can be attached and bonded in a high-vacuum atmosphere. Alternatively, when the structure of the display permits, the cathode electrode 10 and the anode panel 20 can be attached and bonded without any frame.
The cathode panel 10 and the anode panel 20 have a gap of approximately 0.1 to 1 mm between them. A high voltage (for example, 5 kV) is applied to the anode electrode 24 of the anode panel 20. In such a display, a discharge sometimes occurs between the gate electrode 14 provided in the cathode panel 10 and the anode electrode 24 provided in the anode panel 20, and in some cases, the quality of the displayed image is greatly impaired and the lifetime of the display is decreased. The mechanism of discharge occurrence in the vacuum space is assumed to be as follows. First, emission of electrons or ions from the electron emission electrode 16A under an intense electric field triggers a discharge, energy is supplied to the anode electrode 24 from the anode-electrode driving circuit 27 to locally increase the temperature of the anode electrode 24, an occlusion gas inside the anode electrode 24 is emitted or a material itself constituting the anode electrode 24 evaporates, and the small-scale discharge grows to a large-scale discharge (for example, spark discharge).
For suppressing a discharge between the anode electrode 24 and the gate electrode 14, it is effective to suppress the emission of electrons or ions that are to trigger the discharge, while it is required to control particles very strictly. Further, importantly, the anode electrode, the gate electrode, the cathode electrode, etc., have no projection that constitutes a start point of a discharge. However, it involves large technical difficulties to carry out the above particle control in the production process of the display or to control the production process of the display so as to make those various electrodes free of the projections.
In a cathode ray tube, when a sharp projection is present in grid electrodes, etc., constituting an electron lens, an abnormal discharge occurs in the operation of the cathode ray tube. For preventing the above abnormal discharge, a knocking treatment is carried out in the production process of the cathode ray tube. In the knocking treatment, a discharge is caused to occur in a portion that is liable to cause a discharge, such as sharp projection portions, etc., of the grid electrodes, etc., to fuse and remove the projection portions, etc. To the best of the present inventor's knowledge, there is no case where a treatment such as the above knocking treatment in the production of a cathode ray tube is applied to the production of a cold cathode field emission display.
For making tips of cathodes a uniform curvature after completion of a cold cathode field emission display, Japanese Patent No. 3094459 discloses the technique of applying a predetermined voltage to the cathodes to cause field evaporation from the tips. However, the above Japanese Patent does not refer to any knocking treatment technique.
It is therefore an object of the present invention to provide a method of effectively removing projections that are to constitute discharge start points from various electrodes constituting a flat-type display device, after completion of the flat-type display device or during the production of the flat-type display device (before assembly of the flat-type display device).